The continued growth and industrialization of the country demands an increase in the amount of electrical power supplied. These higher urban load current densities in conjunction with the scarcity of available space for substation construciton in urban areas present a problem for power distribution systems. In the past, larger loads have been accommodated by increases in the size of substation circuit-breakers. However, for current connection and disconnection, it is desirable to replace these larger circuit-breakers with smaller devices to meet the increasing demand for electrical power.
Load-breaker-disconnecting-switches as a smaller alternative to the larger circuit-breakers are well known in the art. Some earlier load-breaker-disconnecting-switches employed a circuit interrupter electrically in series with a disconnecting switch and mechanically linked to operate in concert. This combination increased the current disconnecting capacity of the load-breaker-disconnecting-switch without a corresponding increase in size.
Modern high current circuit-breakers are reliable and perform their duties adequately. However, they are physically large and expensive. Where space is a limiting factor, circuit-breakers must acommodate current disconnection requirements in the available space or be replaced by a more space efficient current disconnecting device. Therefore, it is highly desirable to have circuit interrupters which have increased current connection and disconnection capability without increased physical size to replace the corresponding capacity circuit-breakers.
Over the past few years, the circuit interrupter coupled to a disconnecting switch combination has been replaced by a modern circuit interrupter which can connect and disconnect current without the necessity of a series disconnecting switch. This has been accomplished by constructing circuit interrupters which extinguish the arc drawn on disconnection with a jet of a highly insulating gas such as sulfur-hexafluoride. These circuit interrupters are called puffer-type circuit interrupters because of the jet or puff of gas used to extinguish the arc. Because the circuit interrupters are filled and sealed with a gas more insulating than air, a smaller contact distance is required to prevent further arcing once the initial arc is extinguished, therefore leading to smaller equipment. Circuit interrupting devices of this type are set forth in U.S. Pat. No. 3,943,314 which issued Mar. 9, 1976 to Frink, U.S. Pat. No. 4,000,387 which issued Dec. 28, 1976 to Milianowicz, U.S. Pat. No. 4,328,403 which issued May 6, 1982 to Frink et al., and U.S. Pat. No. 3,588,407 issued June 28, 1971 to Frink.
These patents disclose circuit interrupters which operate effectively in a confined space and have a low noise level during the interruption. However, the circuit interrupters taught by Frink and Milianowicz puff only a single volume of sulfur-hexafluoride gas upon a single arc to extinguish it. This puffer circuit interrupter design is limited because the volume of puffer gas can only cool and extinguish so many kilo amperes of arc current. Therefore, to increase the current interrupting capabilities of the prior art design, the volume of available puffer gas would have to be increased which would mean either an increase in the length of the interrupter, or an increased cross sectional area of the puffer mechanism leading to an increased diameter of the interrupter. It is desirable to have a puffer type circuit interrupter that has increased power disconnecting capacity yet without an increased physical size.